1. Field of the Invention
The present invention, relates to a package for housing semiconductor elements for the purpose of housing semiconductor integrated circuit elements and the like.
More specifically, the invention relates to a package for housing semiconductor elements that can accurately electrically connect each electrode of semiconductor integrated circuit elements to external electronic circuits.
2. Related Art
In the past, packages for housing semiconductor elements, in particular, semiconductor integrated circuit elements such as LSI (large-scale integrated circuits), were generally made of electrical insulating materials like alumina ceramic and comprised an insulating base having a depression at nearly the center section on top of the packages for housing the semiconductor integrated circuit elements, a plurality of metallized wiring layers formed of high melting point metallic powders such as tungsten or molybdenum led away from the periphery of the depression of the insulating base and extending to the lower surface thereof, a plurality of connection pads formed on the lower surface of the insulating base which are electrically connected to the metallized wiring layer, ball terminals consisting of solder (brazing filler) hard-soldered to the connection pads, and a lid.
Such packages for housing semiconductor elements become a semiconductor device that can be fabricated as a product by attaching the semiconductor integrated circuit elements to the bottom surface of the depression of the insulating base using an adhesive consisting of materials such as glass or resin; electrically connecting each electrode of the semiconductor integrated circuit elements to the metallized wiring layer by means of bonding wires while joining a lid to the upper surface of the insulating base using a sealant such as glass or resin; and hermetically sealing the semiconductor integrated circuit elements inside a container consisting of the insulating base and the lid.
Such semiconductor devices are operably mounted on an external electronic circuit board by installing ball terminals, which are formed of solder hard-soldered to the connection pads on the lower surface of the insulating base, on the wire conductor of the external electronic circuit board to make contact each other; thereafter fusing the ball terminals at about 150.degree. C. to 250.degree. C.; and thereby joining the ball terminals to the wire conductor. Simultaneously, each electrode of the semiconductor integrated circuit elements housed inside the package for housing semiconductor elements is electrically connected to the external electronic circuit by means of a metallized wiring layer and the ball terminals.
However, in these packages for housing semiconductor elements in the prior art, the coefficient of thermal expansion of the insulating base made of alumina ceramic was on the order of 6.5.times.10.sup.-6 /.degree.C., whereas an external electronic circuit board, which is generally made of glass epoxy, has a coefficient of thermal expansion of from 2.times.10.sup.-5 /.degree.C. to 4.times.10.sup.-5 /.degree.C. Because there was a large difference between the two coefficients, when the semiconductor integrated circuit elements were housed inside the package for housing semiconductor elements followed by being operably mounted on the external electronic circuit board and, heat generated while the semiconductor integrated circuit elements are operated was repeatedly applied to both the insulating base and the external electronic circuit board, a large thermal stress occurred between the insulating base of the package and the external electronic circuit board due to the difference of both coefficients of thermal expansion. This stress acted on the peripheral portion of the connection pads on the lower surface of the insulating base to separate the connection pads from the insulating base. A defect that occurred as a result of this was that, over a long period of time, each electrode of the semiconductor integrated circuit elements housed inside the package for housing semiconductor elements could not be electrically connected to the designated external electronic circuits.
As a further example of the package for housing semiconductor elements in the prior art, packages using ball terminals hard-soldered to the connection pads by means of a brazing filler have been known to be used in place of ball terminals which consist of solder brazer mounted to the connection pads.
Such semiconductor devices are operably mounted on the external electronic circuit board by installing ball terminals, which are hard-soldered to connection pads on the lower surface of the insulating base, on the wire conductor of the external electronic circuit board to make contact each other and by joining the both by solder. Simultaneously, each electrode of the semiconductor integrated circuit elements housed inside the package for housing semiconductor elements is electrically connected to the external electronic circuit by means of the metallized wiring layer and ball terminals.
However, these packages for housing semiconductor elements in the prior art had a defect in that the semiconductor elements housed inside could not accurately and reliably provide an electrical connection to the external electronic circuit because of the fact that the connection pads provided on the lower surface of the insulating base were flat and the terminals joined to the wire conductor of the external electronic circuit board were balllike resulting in variations in the hard solder positions due to movement of the ball terminals which occurred easily with these variations making it impossible to install the terminals while making contact and thus joining the wire conductor of the external electronic circuit board.